Hitherto, as the element member of semiconductor device, photosensitive device for use in electrophotography, image input line sensor, image pickup device, photoelectromotive force device or other various electronic elements and optical elements, there have been proposed a number of amorphous semiconductor films, for instance, an amorphous silicon compensated with hydrogen or/and halogen (e.g., F, Cl)(hereinafter referred to as "A--Si(H,X)"). Some of such films have been put to practical use.
These deposited films have been known to be formed by plasma CVD method wherein a raw material gas is decomposed by subjecting it to the action of an energy of direct current, high frequency or microwave to thereby form a deposited film on a substrate of glass, quartz, heat-resistant synthetic resin, stainless steel or aluminum.
Now, in recent years, industrial attention has been focused on a microwave plasma CVD method (hereinafter referred to as "MW-PCVD method") using the microwave glow discharge decomposition.
One representative known apparatus for the formation of a deposited film by way of MW-PCVD method is such that has a structure as shown by a schematic perspective view of FIG. 10 and a schematic cross-section view of the apparatus of FIG. 10 as shown in FIG. 11.
In FIGS. 10 and 11, 1001 is a reaction chamber having a vacuum enclosed structure. 1002 is a dielectric window made of such material as quartz glass, alumina ceramics, that can transmit efficiently the microwave power into the reaction chamber and can retain the vacuum. 1003 is a microwave guide, and comprises mainly a metallic square waveguide. The waveguide is connected through a matching box and an isolator to a microwave power source (not shown). 1004 is an exhaust pipe that one end is open into the reaction chamber 1001 and the other end is connected to an exhaust apparatus (not shown). 1005 is a substrate on which a deposited film is to be formed. 1006 is a discharge space surrounded by substrates.
The formation of a deposited film using this conventional MW-PCVD apparatus is carried out in the following way. That is, the reaction chamber 1004 is evacuated by operating a vacuum pump (not shown) through the exhaust pipe 1004 to adjust the inside of the reaction chamber to a vacuum of 1.times.10.sup.-7 Torr or less. Then, a heater 1007 is actuated to heat the substrate 1005 with a desired temperature suitable for the formation of a deposited film, and the substrate is kept at this temperature. Thereafter, for example, in the case of forming an amorphous silicon deposited film, silane gas, hydrogen gas and like raw material gas are introduced through a gas introducing means (not shown) into the reaction chamber. Simultaneously, a microwave with frequency of 500 MHz, preferably 2.45 GHz is generated by the microwave power source (not shown), and is introduced through the waveguide 1003 and the dielectric window 1002 into the reaction chamber 1001. Thus, the gas in the reaction chamber 1001 is activated and dissociated to form a deposited film on the surface of the substrate. At this time, the substrate 1005 is rotated in the direction of generatrix around the central axis to form a deposited film on the substrate.
That is, in the above film forming process, part of the surface of the substrate 1005 to become situated in the front region of the discharge space 1006 will be exposed to an atmosphere containing uniformly distributed plasmas and because of this, a film will be uniformly deposited thereon (this film will be hereinafter called "front film"). On the other hand, other parts of the surface of the substrate 1005 to become situated in the side regions of the discharging space 1006 will be exposed to an atmospheres containing unevenly distributed plasmas, so that films to be deposited on such other parts of the surface of the substrate will become uneven accordingly (these films will be hereinafter called "side part films"). The remaining part of the surface of the substrate 1005 to become situated in the non-discharging back region will not be exposed to plasma, so that said part will be maintained without being deposited with any film in said region.
In this respect, the resulting films will often become such that have defects in uniformity and also in homogeneity and that are not satisfactory in characteristics required for the light receiving layer of a photosensitive device, for example.
Therefore, there still remains an unsolved problem for the above-mentioned known MW-PCVD apparatus that it is difficult to stably obtain a desired film suited for use as a constituent layer in semiconductor devices, photosensitive devices for use in electrophotography, image input line sensors, image pickup devices, photoelectromotive force devices or the like.
In particular, there is a problem for the above-mentioned known MW-PCVD apparatus in the case of mass-producing a large size electrophotographic photosensitive member having a light receiving layer of large area that it is extremely difficult to stably obtain a desired large size electrophotographic photosensitive member of uniform quality with a high yield.